Recently, many illumination appliances have been proposed in which LED (Light Emitting Diodes) are employed as light emitting units. As LED mounting methods, there are known COB mounting and package mounting. The COB mounting is practiced, for example, by mounting a semiconductor element to a flat-plate substrate on a surface of which a pattern of lead electrodes is formed using a metal film, electrically connecting the semiconductor element to the lead electrodes, and sealing the semiconductor element with resin.
An LED light emitting device of COB structure is manufactured by electrically connecting an LED element, mounted on a mounting substrate, to wiring lines on the mounting substrate by wire bonding or flip chip mounting, and sealing an LED-element mounted region with light transmissive resin. There is known a manufacturing method of, before resin sealing, disposing an annular frame around a mounting region on the substrate, and filling the light transmissive resin inside the frame for sealing (see, e.g., Patent Document 1).
Hitherto, thermosetting resin made of an organic material and added with inorganic white pigment has been proposed as a composition that can form a solder resist film with a high reflectance (see, e.g., Patent Document 2). The inorganic white pigment has a particle size of, e.g., 0.3 μm or less. However, a liquid material containing the pigment having such a particle size cannot be applied by ink jetting, a dispenser or a spray coater, and it has to be applied by screen printing. Furthermore, heat dissipation performance of an organic material is generally about 0.3 w/m·k and is inferior to that of an inorganic material (e.g. about 1.5 w/m·k of silicon dioxide (SiO2), about 8 w/m·k of titanium dioxide, and about 50 w/m·k of zinc oxide). A wiring substrate using an insulating layer made of an organic material has other problems with heat endurance, deterioration caused by ultraviolet rays, and deterioration attributable to long-term use (i.e., durability).
Of late, a heat pipe (heat spreader) for cooling a heat generating body through evaporation and condensation of a sealed-in coolant has been proposed, and it can be mounted into even a small space. Patent Document 3 proposes a heat pipe including a cooling main body in which a placement portion for arrangement of a device to be cooled is provided in one of an upper plate and a lower plate with one or a plurality of intermediate plates disposed between the upper plate and the lower plate, the cooling main body includes therein a vapor diffusion passage for transferring heat, generated in the device to be cooled upon conversion of the coolant to vapor, to peripheral portions of the cooling main body, and capillary passages disposed in the intermediate plate and constituted to return the coolant condensed in the peripheral portions toward the placement portion, and the placement portion has a recess, which is formed thinner than the other region and in which the device to be cooled is mounted.